After a few releases of no change to the file format this year we have a new file format.
A note from Autodesk:
The DWG format has been updated to provide improvements in the efficiency of open and save operations, especially for drawings that contain many annotative objects and viewports. Additionally, 3D solid and surface creation now uses the newest geometric modeler (ASM) which provides improved security and stability.
Here are some of the last few file formats and which versions of AutoCAD could open those files.
File Format: Versions of AutoCAD:
2004 2004, 2005 and 2006
2007 2007, 2008, 2009
2010 2010, 2011, 2012
2013 2013, 2014, 2015, 2016 and most of 2017
Let's hope that the 2018 dwg file format sticks around as long as the 2013 file format!